We adapt the techniques in Stigler [Ann. Statist. 1 (1973) 472–477] to obtain a new, general asymptotic result for trimmed U-statistics via the generalized L-statistic representation introduced by Serfling [Ann. Statist. 12 (1984) 76–86]. Unlike existing results, we do not require continuity of an associated distribution at the truncation points. Our results are quite general and are expressed in terms of the quantile function associated with the distribution of the U-statistic summands. This approach leads to improved conditions for the asymptotic normality of these trimmed U-statistics.